Amy Caddick went to the salon earlier this year seeking the light locks of Khloé Kardashian—and wound up in the hospital just two days later as a result.

The 25-year-old from Liverpool, United Kingdom, left the salon feeling confident in her new ombré look, but woke up the next morning alarmed to see her scalp and forehead inflamed.

“I woke up in complete agony,” Caddick explained to the Daily Mail (which has photos of Caddick's ordeal). “My skin felt raw and tender.” Matters only got worse from there: The following day, the swelling moved down her face, sealing her eyes shut and beginning to close her airway.

Caddick was rushed to the hospital for treatment, where she was told that the inflammation could eventually have blocked her airway completely, ultimately suffocating her. Turns out, she'd had an anaphylactic reaction to the hair color used to dip-dye her strands.

“I was in shock. Never in a million years did I think treating myself to a new hairdo would turn out this way,” Caddick told the Daily Mail. “You expect to come out of a hair salon feeling like a million dollars—not hooked up to an IV drip.”

It took over a week for the swelling to let up, and she now reports “thinner, patchier” hair than before.

An allergy to hair dye is rare, but, as seen in Caddick's case, can be just as serious as allergies to more common culprits like nuts or shellfish. Sufferers develop reactions when skin comes in contact with p-phenylenediamine, a chemical found in most dyes (both in-salon and over-the-counter).

The result: Symptoms ranging from a temporary, mild burning or slight redness all the way up to swelling, blisters, hives, and pustules. (Some reactions may be mild the first time it happens, but can quickly turn serious with the next exposure.) Some, like Caddick, can experience a potentially deadly reaction, if the swelling occurs in the throat. Treatment for mild reactions can include over-the-counter antihistamine pills or creams, but if you're having trouble breathing you need to get to the hospital, stat.

If you’re coloring your hair for the first time or you've noticed skin sensitivities after your last few appointments, ask your stylist to do a patch test. She'll put just a bit of dye on your skin and have you wait 48 hours to see if you develop a reaction to it. As Caddick's story proves, skipping the patch test can cost you. “This oversight nearly cost my life,” she said.